Method for reading data from a magnetic recording tape

ABSTRACT

A method for reading data from a magnetic recording tape having multiple adjacent data tracks according to one embodiment includes simultaneously detecting signals from a plurality of read devices, at least some of the read devices being positioned over multiple data tracks while other of the adjacent read devices are positioned over single data tracks; determining which of the read devices is positioned over a single data track; and simultaneously reading data from the data tracks using only those read devices over the single data tracks. A method for reading and writing data to a magnetic recording tape according to another embodiment includes simultaneously writing data tracks to a magnetic medium; and simultaneously reading the data tracks on the magnetic medium using a plurality of adjacent read devices; wherein the number of the adjacent read devices is at least twice the number of the adjacent write devices.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/216,615 to Czarnecki et al., filed Aug. 30, 2005, and which is hereinincorporated by reference.

This application is related to U.S. patent application Ser. No.11/215,602 to Berman et al., entitled “System and Method forDeconvolution of Multiple Data Tracks” filed Aug. 30, 2005, and which isherein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to tape drive heads, and moreparticularly, this invention relates to a write and read device arraywhere widths of the read devices are smaller than widths of the writedevices or data tracks.

BACKGROUND OF THE INVENTION

Data is stored on magnetic media such as tape by writing data in amultiplicity of linear tracks. The tracks are separated along thetransverse direction of the tape and a given track runs longitudinallyalong the tape.

In order to increase the amount of data that can be written for a giventape width, efforts have been made to make data tracks adjacent oneanother. The most common method for writing is to use writers that arespaced apart by a predetermined distance. During writing, several tracksare written simultaneously, with a gap positioned between each track andthe tracks adjacent thereto. Then, when writing in the oppositedirection, the head steps to one side and writes additional tracks,overlapping the previous tracks by a certain amount (called“shingling”).

The reader is typically slightly smaller than the writer, is alignedtherewith, and is reading one single track. This is called “write wide,read narrow.” Because the reader is narrower than the writer, the readerwill tend not to read adjacent tracks in spite of the “wobble” of thetape relative to the reader as the tape moves across the head.

FIG. 1 illustrates a typical multitrack tape head 100 having a multitudeof read elements 102 and write elements 104, where the read elements 102are aligned with the write elements 104. Servo elements 106 (one shown)flank the read elements 102 and are used to sense servo tracks on themedium to keep the head 100 aligned over a data track duringreading/writing.

A major drawback to this traditional “shingling” method, however, isthat wobble increases the probability of overwriting adjacent datatracks during writing the reverse direction. As the track widthdecreases, the amount of wobble (or track mis-registration) needs todecrease proportionally. As the track width is decreasing with futuregenerations, it is becoming more difficult to decrease the trackmis-registration sufficiently to avoid overlap of readers on multiplewritten tracks.

One solution calls for writing adjacent data tracks in the samedirection. Writers positioned adjacent each other simultaneously writemultiple tracks. An advantage of this type of system is that the chanceof overwriting data tracks due to wobble is eliminated for the group ofsimultaneously written adjacent tracks. Further, because all tracks arewritten simultaneously, as the tape wobbles, all tracks follow the samewobble.

Simultaneous data tracks work well if the head can precisely positionits readers over each data track. However, servo tracks are typicallywritten to the tape prior to writing any data. So, during readback, eventhough the head is following the servo tracks, errors occur due towobble of the written data tracks and the inherent wobble duringreadback, and may even be exacerbated by a wobbly servo track. Theerrors can result in a particular reader reading two or more trackssimultaneously, especially where track spacing is minimal oroverlapping. The resultant signal is noisy and may make extraction ofthe data impossible.

To resolve this problem and provide other advantages, the embodiments ofthe invention disclosed herein proposes providing multiple readers perdata track, where the readers have less than half the width of thewriters or data track width.

SUMMARY OF THE INVENTION

A method for reading data from a magnetic recording tape having multipleadjacent data tracks according to one embodiment includes simultaneouslydetecting signals from a plurality of read devices, at least some of theread devices being positioned over multiple data tracks while other ofthe adjacent read devices are positioned over single data tracks;determining which of the read devices is positioned over a single datatrack; and simultaneously reading data from the data tracks using onlythose read devices over the single data tracks.

A method for reading and writing data to a magnetic recording tapehaving multiple adjacent data tracks according to another embodimentincludes simultaneously writing data tracks to a magnetic medium; andsimultaneously reading the data tracks on the magnetic medium using aplurality of adjacent read devices; wherein the number of the adjacentread devices is at least twice the number of the adjacent write devices.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is a representative view of a typical prior art multitrack tapehead having a multitude of read and write elements as seen from the tapebearing surface.

FIG. 2 illustrates a module portion of a tape head.

FIG. 3 is a representative view of the read and write elements of themodule of FIG. 2 taken from Circle 3 of FIG. 2 and as seen from the tapebearing surface.

FIG. 4 illustrates a head for a read-while-write bidirectional lineartape drive in use.

FIG. 5 is a simplified schematic of multiple read devices which overlapwritten tracks on a magnetic recording tape.

FIG. 6 is a simplified schematic of multiple read devices which overlapwritten tracks on a magnetic recording tape.

FIG. 7 is a process diagram of a method for selecting read devicesaccording to one embodiment.

FIG. 8 illustrates a tape drive which may be employed in the context ofthe method of FIG. 7.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description is the best embodiment presently contemplatedfor carrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.Further, particular features described herein can be used in combinationwith other described features in each of the various possiblecombinations and permutations.

FIG. 2 illustrates a module 200 carrying multiple read devices (alsocalled readers, sensors, read elements, etc.) and write devices (alsocalled writers, write elements, etc.). As shown, the write devices 201and read devices 202 are positioned towards the middle of the module200. In order to increase the stability of the module 200 for thesuitable use thereof, the module 200 is attached to a beam 206 of somesort formed of a rigid material. Such beams 206 are often referred to asa “U-beam.” A closure 208 is often attached in view of the benefits itaffords in resultant heads.

FIG. 3 is a representative view of the read devices 202 and writedevices 201 of the module 200 according to one embodiment of the presentinvention. As shown, the width (W_(R)) of the read devices 202 is muchless than the width (W_(W)) of the write devices 201 and consequentlythe width (W_(T)) of the written track 302 (shown in dotted lines torepresent the width of data tracks on the tape). For example, the width(W_(R)) of the read devices is preferably half or less than half ofW_(W). The spacing (S_(R)) between centerpoints of the read devices 202is significantly less than the spacing (S_(W)) between centerpoints ofthe write devices 201 as measured in a direction transverse to thedirection of tape travel. Also, note that more read devices 202 arepresent than write devices 201. The importance of these aspects will bediscussed in more detail below, and are described here with reference tothe drawings to provide context to the concepts.

One skilled in the art will appreciate that the configuration of writeand/or read devices 201, 202 can vary. Particular examples includeinterleaved configurations where the read and write devices 201, 202alternate, piggybacked configurations where the read and write devices201, 202 are formed one above the other on the same substrate in thetape travel direction, etc.

FIG. 4 illustrates a head 400 for a read-while-write bidirectionallinear tape drive in use. “Read-while-write” means that the read elementfollows behind the write element. This arrangement allows the data justwritten by the write element to be immediately checked for accuracy andtrue recording by the following read element.

The head 400 of FIG. 4 is formed by coupling two modules 200 of the typeshown in FIG. 2. Specifically, in FIG. 4, two modules 200 are mounted onU-beams 206 which are, in turn, adhesively coupled. Cables 402 arefixedly coupled to pads in communication with the read and write devices201, 202 (FIG. 2). The tape 404 wraps over the modules 200 at apredetermined wrap angle α.

It should be noted that the two-module tape head 400 of FIG. 4 isrepresentative only, as the precepts of the present invention can beimplemented in any type of head where multiple tracks of information canbe written and subsequently read.

One skilled in the art will appreciate that the configuration of writeand/or read devices 201, 202 can vary. For instance, one module can haveall write devices 201, while the other module can have all read devices202. Another example would be to have a plurality of write devices 201and read devices 202 all aligned linearly perpendicular to the directionof tape movement. It should also be understood that the number of readand write devices described herein are provided by way of example only,and can be increased or decreased per the desires of the designer,system requirements and capabilities, etc.

Another variation includes a head having only a single module of readand write devices that provides all of the read/write functionality. Ofcourse the shape of the module may be different than the module 200shown in FIG. 2. One skilled in the art will appreciate how to create asingle module design using traditional head designs.

According to a preferred embodiment, a multiplicity of data patterns or“tracks” are written onto a medium, such as a magnetic recording tape,using a multiplicity of adjacent write devices with a width W_(W). Thesignals are then read by a multiplicity of read devices whose width(W_(R)) is half or less than half of W_(W). A given embodiment includesmultiple read devices R(1), R(2), . . . , R(N_(R)), where N_(R) is thenumber of readers which overlap written tracks T(1), T(2), . . . ,T(N_(W)), where N_(W) is the number of writers) on a magnetic recordingtape where W_(R) is less than or equal to half of W_(W). Twoillustrative embodiments are shown in FIG. 5. In the embodiment ofscenario (a), S_(R)=S_(W)/2 with W_(R)≦W_(W)/2. In the embodiment ofscenarios (b) and (c), S_(R)=S_(W)/4 with W_(R)≦W_(W)/4.

In scenario (a) where S_(R)=S_(W)/2, a simple algorithm is to keep onlythe signals which are on a single given track. In scenario (a) shown forW_(R)=W_(W)/2, read devices R(3) and R(5) would be maintained and wouldbe associated with written tracks T(1) and T(2) respectively. Inpractice, it might be best to have W_(R) be slightly less than W_(W)/2,with S_(R)=S_(W)/2. The choice of which read devices to use can bedetermined by the lack of signal on the outer read devices (assuming nodata written outside the tracks T). R(1) and R(7) would not register apattern, while R(2), R(3), R(4), R(5), and R(6) would register a signal.Because the system knows that if R(1) and R(7) do not register apattern, R(3) and R(5) must be on the data track based on the dimensionsof the data tracks and head, the signal from R(3) and R(5) is used andthe signal from R(2), R(4), and R(6) can simply be discarded. Note thatthe signals from R(2) and R(6), though partial, could also be used toenhance the signal if desired. Similarly, if R(1) and R(2) do notregister a pattern, and R(7) registers a pattern (e.g., due to wobble),the system can still determine which read devices are over the tracksand can, for instance, then use the signal from R(4) and R(6) to readT(1) and T(2). The system can also note the offset and adjust theposition of the head so that the read devices are once again positionedas shown in scenario (a) of FIG. 5.

Scenarios (b) and (c) of FIG. 5 depict the case where S_(R)=S_(W)/4 withW_(R)≦W_(W)/4. In practice, it might be best to have W_(R) be slightlyless than W_(W)/4, but to have S_(R)=S_(W)/4. In scenario (b), nosignals will be detected on read devices R(1), R(2) or R(11) so R(3) toR(6) would be associated with T(1) and R(7) to R(10) would be associatedwith T(2). This method of deconvoluting the read signals would enableunambiguous determination of the signals from a given written track. Inscenario (c), the system will detect no signal from R(1) and R(11), buta partial signal from R(2) and R(10). Accordingly, the system will usethe signal from R(3) to R(5) to read T(1) and R(7) to R(9) to read T(2).The read signals which come from an overlap of the two tracks (R(4) fromscenario (a), and R(6) from scenario (c)) could also be used byextending the concept given in the copending application incorporated byreference herein.

While this example shows only two written data tracks and a small numberof read devices, one skilled in the art will appreciate that many moredata tracks, read devices, etc. may be present in a particular system.

The determination of which read device to use for a given track can bemade at least in part by using the signal intensities read from one ormore guide bands adjacent a group of data tracks. Because the positionof the guide bands is known with respect to the data tracks, the systemcan determine which read devices are over a guide band and which readersare over which data tracks. A simple way to create the guide band, andthe preferred method, is to do a DC erase while writing. A DC eraseessentially creates a “dead” region which produces no signal duringreadback. Any read device over the DC erased guide band will produce nosignal. Another option to create the guide band is to write a monotoneor fundamental harmonic instead of the DC erase. A reader producing asignal corresponding to the monotone or fundamental harmonic will thenbe known to be at least partially over the guide band. A further methodis to use an AC erase. One skilled in the art will appreciate the manyways that guide bands can be added to the tape.

When the system is set up properly according to the preferredembodiment, there will always be a read device in the guide band oneither side of the data group. And because the width W_(R) of the readdevice is equal to or less than one half the width W_(W) of the writedevice or data track width W_(T), one read device will always beentirely on a particular data track even if other read devices overlaptwo tracks.

During reading, the read devices over the guide band will get no signalat all (if dead band), or will detect the harmonic or other pattern. Theinner read devices will, however, produce data signals.

FIG. 6 illustrates an example of three adjacent groups of written tracksT. In this example, each group has four written tracks. A “dead” guardband G is positioned between each group of written tracks. All trackswithin a given group are written simultaneously by four adjacent writedevices. An illustrative write device array would have six writedevices, four for data and two to write the guide bands for a particulardata group. Flanking guide band write devices is the most reliable,particularly where the tape has been previously written to. The arraycould also implement only one write device to generate one guard band,thus relying on the guard band created by the next pass of writing toavoid overlapping previously written tracks. The width of the guard bandwriter(s) might be chosen to be larger than the track writers.

In the example of FIG. 6, S_(R)=S_(W)/2 with W_(R)≦W_(W)/2. Also, thenumber of read devices R in this example is 12, which is twice thenumber of write devices mentioned in the previous paragraph, and threetimes the number of write devices that write the data tracks. By havingmore than twice the number of read devices as write devices, at leastone read device will be over the guard band at any given time. Inscenario (a) of FIG. 6, read devices R(4), R(6), R(8) and R(10) areassociated with tracks T(1) to T(4) respectively for written Data Group2. The determination of which read device should be associated withwhich write device is made by noting that R(2) and R(12) have no signalsand R(1), R(3) and R(11) have partial signals.

In scenario (b) of FIG. 6, read devices R(3), R(5), R(7) and R(9) areassociated with tracks T(1) to T(4) respectively for written Data Group2. The determination of which read device should be associated withwhich write device is made by noting that R(1) and R(11) have no signalsand R(2), R(10) and R(12) have partial signals.

In scenario (c) of FIG. 6, read devices R(2) and R(3) are associatedwith track T(1), R(4) and R(5) are associated with track T(2), R(6) andR(7) are associated with track T(3), and R(8) and R(9) are associatedwith track T(4) for written Data Group 2. The determination of whichread device should be associated with which write device is made bynoting that R(1), R(10), and R(11) have no signals and R(12) has partialsignals.

The guide band may be the same size as the data tracks, but does notnecessarily need to be. The choice of the width of the guard bandbetween groups of written tracks where no signals are written will needto be carefully chosen. Decisions on the choice of the read devicewidth, read device spacing, and the width of the guard band must be madewhich include considerations such as (1) optimizing the data density;(2) optimizing the signal-to-noise ratio (SNR); (3) how well the drivecan maintain the alignment of the positioning of the read devices withthe written tracks; (4) ease of implementation in the drive constraintsof data processing; and (5) ability to handle the signal output to thedrive.

One practicing the invention should also be careful to not allow thewrite device creating the guide band to overlap an already-written datatrack by too much. Thus, it may be desirable to space the guide band ina subsequent data group slightly away from the nearest data track of aprior-written data group.

As mentioned above, during reading of the media, the overall systemreceives a data signal from the read devices. Besides using theinstantaneous read signal, a running average of the signal changes canbe used to determine which of the read devices are entirely on a track,and which are not. The following signals are possible:

-   -   read devices in guide band will get no signal (assuming dead        area)    -   read devices on track will get data signal    -   read devices partially over data track and guide band will have        partial data signal    -   read devices over two data tracks will have signal representing        the two tracks

From some or all of this data, the system can determine which readdevice(s) are entirely on a particular track. The system can then usesignal from the read device(s) which are on the track and discard theremaining signals. For instance, signals from read devices over twotracks may be discarded. Alternatively, the signal from each track maybe deconvoluted as described in the US patent application entitled“System and Method for Deconvolution of Multiple Data Tracks” which hasbeen incorporated by reference above.

FIG. 7 depicts a process 700 for selecting which read devices to use toread data tracks. The following illustrative process assumes read devicewidths are equal to or slightly less than one half the width of the datatrack, a read element which is positioned over only the guide bandyields no signal other than noise. The process analyzes the read devicesfrom the outside position in based on their readback signal.

At decision 702, the read devices are sensed for a signal. If no signalis detected, the read device(s) are marked as being on a guide band inoperation 704. Thus, alternate readers will be on track. If reader n ison the first guide band, readers n+2m (n and m are integers) will be ontrack m. In operation 706, all other read devices are marked as at leastpartially over data tracks.

At decision 708, the signal from the read device(s) innerly adjacent tothe read device(s) over the guide band are analyzed for full signalstrength. If a partial signal is detected, the read device is marked aspartially on a data track and partially over a guide band in operation710. In operation 712, the data is discarded, and in operation 714, thesignal from the next read device innerly adjacent thereto is used toread data from the outer data bands. If a full data signal (or above apredetermined threshold) is found, then the signal can be used to readdata from the outer data tracks. See operation 716.

In operation 718, the signal from the read device innerly adjacent tothe previously-read read device is detected. At decision 720, the signalfrom the read device is compared to the previously-read read device. Inoperation 722, if a partial signal is found that includes elements thatare the same as the signal from the previously-read read device andelements that are different than the signal from the previously-readread device, the signal is discarded because the read device is over twotracks. If the signals are different, the signal is used to read datafrom the data track in operation 724. [Note that this also works forembodiments where more than one read device will fit within a giventrack width. In the case where two read devices are entirely over asingle data track, the first read device signal analyzed will be used,and the signal from the second device can be discarded.]

Operations 718-724 are repeated for each read device. The entire processshould be repeated at least periodically to account for any wobble.

One skilled in the art will appreciate that other processes can be usedto determine the positioning of the read devices. For instance, considerthe following example assuming no expansion and contraction of the tape,W_(R)=W_(W)/2, and all readers are read simultaneously. Each of thereaders are grouped into odd or even groups. If an odd guide reader ispositioned over a guide band, the output from the odd readers can beused to read the data tracks. Likewise, if an even guide reader ispositioned over a guide band, the even readers can be used to read thedata tracks. This is a very simple example, but functions adequately.

Again, one skilled in the art will appreciate that more complex schemescan be employed, and may be desirable. Because of dropouts (wheresignals decrease due to imperfections in the tape magnetic coatings)more complicated schemes can be employed which utilize the signal levelsfrom all readers. Scenario (a) of FIG. 6 can be used for illustration.R(2) and R(12) will give no signal. R(3) and R(11) will provide partialsignals and R(4) through R(10) should give full signals. Thus, R(4+2m)where (m=1 to 4) will be on tracks m (1 to 4) respectively. Because ofimperfections in the tape magnetic coating, the signals from one or moreof the readers R(3) through R(11) may be weaker than expected or may below at that time point due to the lack of a transition at that timepoint. Using die running average information of reader-to-tracklocation, the total width of the written track can greatly improve thereader-to-track correspondence.

One skilled in the art will also appreciate that read device selectioncan be done via integration, and even instantaneously. The particularmethod to select active read devices will, of course, depend on theconfiguration of the system in which implemented.

One practicing the invention and creating a new process should also keepin mind that the data group will always be spaced the same distance fromthe guide band, as long as the guide band is written concurrently withthe data tracks. Once it is known that a read device is positioned overa guide band, the positions of the other read devices relative to theguide band and data tracks can be readily determined. Accordingly, asimpler process would be to merely detect which read device(s) are overthe guide band, and then determine the positions of the remaining readdevices, and/or select from which read devices to use signal, based onthe expected boundaries of the data tracks relative to the guide band.Deformation of the tape due to creep from use or age or expansion andcontraction from temperature or humidity changes could change the widthof previously written tracks. If the number of tracks in a group (N_(G))is large and the and the tape expands sufficiently, it is possible thata more complicated algorithm than using alternate readers would benecessary to determine the reader-to-written track correlation. A personskilled in the art will make the necessary adjustments.

The selection process to determine which heads to take signal fromshould be continuously performed, at least with respect to determiningwhich read devices are fully and/or partially over the guide bands, toaccount for wobble.

As mentioned above, because the read device width is equal to or lessthan one half the width of the write device or data track, one readdevice will always be entirely on a particular data track even if otherread devices overlap two tracks. Moreover, if the read devices are onethird the width of the write device or track width, then two readdevices will always be positioned over a particular data track. If theread devices are one fourth the width of the write device or trackwidth, then three read devices will always be positioned over aparticular data track. Accordingly, reducing the width of the readdevices allows for more read devices to be positioned over a single datatrack, and thus, higher resolution.

An additional benefit of the system and method is that by using multipleread devices having narrow widths, the system can read tapes created byvarious write devices having different write device widths. Forinstance, the system can read not only data from a tape written by adrive from manufacturer A having write devices of width X, but also atape written by a drive from manufacturer B having write devices afraction or multiple of width X (e.g., 0.65X or 2X). The system wouldhave enough read devices present to read each track in a particular datagroup on the tape, as well as identify a guard band (or equivalent) fromwhich to make the determination of which read devices are on aparticular track. If the guard band is a “dead” zone, the determinationwould be relatively easy. If the guard band is a servo pattern, theparticular servo pattern used by manufacturer A or B may need to beloaded into the system. Also, information relating to the number oftracks per data group, how data is encoded when written on the tape,etc. can be loaded for a particular manufacturer or format.

FIG. 8 illustrates a tape drive which may be employed in the context ofthe method 700 of FIG. 7. While one specific implementation of a tapedrive is shown in FIG. 8, it should be noted that the embodiments of theprevious figures may be implemented in the context of any type of drive(i.e. hard drive, tape drive, etc.)

As shown, a tape supply cartridge 820 and a take-up reel 821 areprovided to support a tape 822. Moreover, guides 825 guide the tape 822across a bidirectional tape head 826. Such bidirectional tape head 826is in turn coupled to a controller assembly 828 via a compression-typeMR connector cable 830. The actuator 832 controls position of the head826 relative to the tape 822.

A tape drive, such as that illustrated in FIG. 8, includes drivemotor(s) to drive the tape supply cartridge 820 and the take-up reel 821to move the tape 822 linearly over the head 826. The tape drive alsoincludes a read/write channel to transmit data to the head 826 to berecorded on the tape 822 and to receive data read by the head 826 fromthe tape 822. An interface is also provided for communication betweenthe tape drive and a host to send and receive the data and forcontrolling the operation of the tape drive and communicating the statusof the tape drive to the host, all as understood by those of skill inthe art.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1. A method for reading data from a magnetic recording tape havingmultiple adjacent data tracks, the method comprising: simultaneouslydetecting signals from a plurality of read devices, at least some of theread devices being positioned over multiple data tracks while other ofthe adjacent read devices are positioned over single data tracks;determining which of the read devices is positioned over a single datatrack; and simultaneously reading data from the data tracks using onlythose read devices over the single data tracks.
 2. A method as recitedin claim 1, further comprising determining which of the read devices ispositioned over a guide band, wherein the determination of which of theread devices is positioned over one of the data tracks is based at leastin part on the position of the read devices relative to the guide band.3. A method as recited in claim 1, wherein a width of each of the readdevices is less than or equal to one half a width of the data tracks. 4.A method as recited in claim 1, wherein the number of read devices ismore than twice the number of write devices.
 5. A method as recited inclaim 1, wherein a spacing between centerpoints of the read devices isless than or equal to one half a spacing between centerpoints of thewrite devices.
 6. A method for reading and writing data to a magneticrecording tape having multiple adjacent data tracks, the methodcomprising: simultaneously writing data tracks to a magnetic medium; andsimultaneously reading the data tracks on the magnetic medium using aplurality of adjacent read devices; wherein the number of the adjacentread devices is at least twice the number of the adjacent write devices.7. A method as recited in claim 6, further comprising determining whichof the read devices is positioned over a guide band, wherein thedetermination of which of the read devices is positioned over one of thedata tracks is based at least in part on the position of the readdevices relative to the guide band.
 8. A method as recited in claim 6,wherein a width of each of the read devices is less than or equal to onehalf a width of the data tracks.
 9. A method as recited in claim 6,wherein the number of read devices is more than twice the number ofwrite devices.
 10. A method as recited in claim 6, wherein a spacingbetween centerpoints of the read devices is less than or equal to onehalf a spacing between centerpoints of the write devices.
 11. A methodas recited in claim 6, wherein the adjacent read devices are alignedalong a straight line.